Polymer hydrogenation process

ABSTRACT

Selective hydrogenation of the carbon-carbon double bonds of conjugated diene copolymers is effective homogeneous solution in an organic solvent in the presence of certain divalent ruthenium carbonyl complex catalysts. The ruthenium catalysts have the general formula: 
     
         Ru(CO)HA(Z).sub.3                                          (1) 
    
     wherein A is a halogen atom, most preferably chlorine, or a hydrogen atom and Z is --PR 1  R 2  R 3  in which R 1 , R 2  and R 3  are the same or different and are selected from alkyl and aryl groups, preferably all the phenyl group, or have the general formula: 
     
         Ru(CO)XY(Z).sub.2                                          (2) 
    
     wherein X is a carboxylate group, particularly ClCH 2  COO--, Cl 2  CHCOO--, Cl 3  CCOO--, F 3  CCOO--, CH 3  COO--, C 6  H 5  COO-- or p--ClC 6  H 4  COO--, Y is a halogen atom, preferably a chlorine atom or a bromine atom, or a hydrogen atom or a carboxylate group, Z is as defined above; or have the general formula: 
     
         Ru T(CO)(NO)(Z).sub.2                                      (3) 
    
     wherein T is a halogen atom, preferably a chlorine or bromine atom, and Z is as defined above; or have the general formula: 
     
         Ru T(NO)(Z).sub.2                                          (4) 
    
     wherein T and Z are as defined above; or have the general formula: 
     
         Ru H(NO)(Z).sub.3                                          (5) 
    
     wherein Z is as defined above; or have the general formula: 
     
         Ru (NO).sub.2 (Z).sub.2                                    (6) 
    
     wherein Z is as defined above.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending United States patent application Ser. No. 070,023 filed July 6, 1987.

FIELD OF INVENTION

The preent invention relates to the selective hydrogenation of the carbon-carbon double bonds in a copolymer of a conjugated diene and one or more copolymerizable monomers using a particular catalyst.

BACKGROUND TO THE INVENTION

Several homogeneous and heterogeneous processes based on rhodium or palladium metal catalysts have been proposed and are now being used to hydrogenate carbon-carbon double bonds in acrylonitrile-butadiene copolymers and other similar polymers.

For example, French Pat. No. 2,421,923 discloses the partial hydrogenation of the double bonds in acrylonitrile-butadiene rubber (NBR) over a palladium/charcoal catalyst.

German Offenlegungsschrift No. 3,046,008 discloses the selective hydrogenation of the double bonds in conjugated diene containing polymers such as NBR, wherein the catalyst is palladium and at least one other element on a support which may be silica, alumina or activated carbon.

German Offenlegungsschrift No. 3,046,251 discloses a similar process except that the catalyst support is channel or furnace carbon black.

Published British Patent Application No. 2,070,023A discloses a process for the selective hydrogenation of the double bonds in unsaturated organic polymers such as acrylo-nitrile-butadiene-styrene polymers, when in the form of an aqueous emulsion, using a catalyst such as chloro-tris(triphenylphosphine)rhodium in a hydrocarbon solution.

U.S. Pat. No. 3,898,208 describes a process for hydrogenation of latexes of oil-insoluble polymers of conjugated dienes. The latex is dispersed in a swelling agent for the polymer and hydrogenated in the presence of a catalyst complex which may be a rhodium complex catalyst such as chlorotris(triphenylphosphine)rhodium. The swelling agent must also be a solvent for the catalyst complex.

U.S. Pat. No. 3,700,637 discloses that the double bonds in alternating copolymers of conjugated dienes and unsaturated nitriles may be hydrogenated using catalysts which preferably are homogeneous rhodium halide complex catalysts having the formula L₃ RhX wherein X is halogen and L is an organophosphorus or organoarsenic stabilizing ligand. It is also preferred that an excess of the ligand be used during the hydrogenation, the mole ratio of ligand to rhodium complex being between about 10:1 and about 150:1.

British Pat. No. 1,558,491 discloses the hydrogenation of the double bonds in copolymers of a conjugated diene and an α,β-unsaturated carboxylic acid or derivative thereof, for example acrylonitrile, using as catalyst a homogeneous monovalent or trivalent rhodium halide complex of the formula L₃ RhX_(n) wherein X is chlorine or bromine, n is 1 or 3, and L is a ligand. An additional 5 to 25 weight percent, based on the copolymer of the ligand may optionally be used. The amount of hydrogenation is highly solvent dependent.

U.S. Pat. No. 3,480,659 describes a process for the selective hydrogenation of double bonds in unsaturated monomers containing 2 to 20 carbon atoms using a homogeneous rhodium hydride complex catalyst, for example, hydridotetrakis(triphenylphosphine)rhodium, along with an excess of a complexing ligand, for example triphenylphosphine. The mole ratio of ligand to catalyst is between about 10:1 and about 150:1.

Italian Pat. No. 912,648 discloses that cycloalkadienes and alkadienes may be selectively hydrogenated to the corresponding cycloalkenes and alkenes using a catalyst such as hydridotetrakis(triphenylphosphine)rhodium.

More recently, there issued U.S. Pat. Nos. 4,464,515 and 4,503,196 in which one of us is named as an inventor. U.S. Pat. No. 4,464,515 describes the hydrogenation of carbon-carbon double bonds in copolymers of conjugated dienes and copolymerizable monomers in the presence of a monovalent rhodium hydride complex of the formula RhHL_(1x) in which x is 3 or 4 and L₁ is a first ligand, a second ligand compound L₂ and a solvent for the compound. U.S. Pat. No. 4,503,196 describes the selective hydrogenation in the absence of added ligand and in the presence of a monovalent rhodium hydride complex of the formula RhHL_(x) where, when x is 4, L is a phosphorus compound which is 5-phenyl-5H-dibenzophosphole or a compound of formula PR₁ R₂ R₃ or, when x is 3, L is an arsenic or antimony compound of the formula MR₁ R₂ R₃, wherein M is arsenic or antimony, and wherein R₁, R₂ and R₃ are selected from CH₃, C₂ H₅, C₆₋₁₀ aryl groups and C₇₋₁₂ aralkyl groups.

The advantage of the processes described in the latter two patents is that improved rates of hydrogenation are achieved under relatively mild conditions and that the degree of hydrogenation is relatively insensitive to the amount of solvent used.

However, rhodium is an expensive metal and hence we made an investigation to look for an efficient but cheaper hydrogenation process based on other catalyst materials.

In U.S. Pat. No. 4,631,315, there is described the hydrogenation of nitrile group-containing polymers in a low molecular weight ketone as a solvent using certain ruthenium catalysts having the formula:

    RuX[(L.sub.1)(L.sub.2).sub.n ]

wherein X represents hydrogen or halogen, L₁ represents hydrogen, halogen or optionally substituted cyclopentadienyl, L₂ represents phosphine, bisphosphine or arsine, n is 1, 2 or 3 and [(L₁)(L₂)_(n) ] represents a cyclopentadienyl bisphosphine. The data presented in this patent suggests that free ligand is necessary to achieve acceptable reaction rates.

In published German patent application No. 3,529,252, there is also described the hydrogenation of nitrile group-containing polymers in a low molecular weight ketone using other ruthenium catalysts, this time of the formula:

    RuH.sub.m (COOR.sub.1).sub.n (L).sub.p

wherein R₁ is an alkyl, aryl, cycloalkyl or aralkyl, L represents phosphine or arsine, m is 0 or 1, n is 1 or 3 and p is 2 or 3.

SUMMARY OF INVENTION

In accordance with the present invention, there is provided a novel process for the selective hydrogenation of the carbon-carbon double bonds in a copolymer of a conjugated diene and one or more copolymerizable monomers using certain ruthenium complexes, as described below and which are not described in the aforementioned U.S. Pat. No. 4,631,315 nor in German OS No. 3,529,252.

Accordingly the present invention provides an improvement in a process for the selective hydrogenation of the carbon-carbon double bonds in a copolymer of a conjugated diene and at least one copolymerizable monomer. The improvement comprises effecting the hydrogenation in the presence of at least one divalent ruthenium complex selected from the group consisting of:

(a) a ruthenium complex of the general formula:

    Ru(CO)HA(Z).sub.3                                          ( 1)

wherein A is a halogen atom or a hydrogen atom, Z is a --PR₁ R₂ R₃ group in which R₁, R₂ and R₃ may be the same or different and are selected from alkyl and aryl groups,

(b) a ruthenium complex of the general formula:

    Ru(CO)XY(Z).sub.2                                          ( 2)

wherein X is a carboxylate group, Y is a halogen atom, a carboxylate group or a hydrogen atom, and Z is as defined above,

(c) a ruthenium complex of the general formula:

    RuT(CO)(NO)(Z).sub.2                                       ( 3)

wherein T is a halogen atom and Z is as defined above,

(d) a ruthenium complex of the general formula:

    RuT(NO)(Z).sub.2                                           ( 4)

wherein T and Z are as defined above,

(e) a ruthenium complex of the general formula:

    RuH(NO)(Z).sub.3                                           ( 5)

wherein Z is as defined above, and

(f) a ruthenium complex of the general formula:

    Ru(NO).sub.2 (Z).sub.2                                     ( 6)

where Z is as defined above.

The ruthenium complex catalysts achieve efficient and effective selective hydrogenation of the carbon-carbon double bonds and such selective hydrogenation may be achieved without substantial cross-linking the copolymer, for example, an acrylonitrile-butadiene rubber (NBR).

GENERAL DESCRIPTION OF THE INVENTION

Essential to the present invention is the effecting of selective hydrogenation of carbon-carbon double bonds in NBR, styrene-butadiene rubber and similar copolymers of conjugated dienes and copolymerizable monomers, using particular ruthenium complexes containing carbonyl ligands, or nitrosyl ligands, or carbonyl and nitrosyl ligands. The ruthenium complexes also may contain halide, hydride, phosphine and/or carboxylate ligands.

One class of such ruthenium complexes which may be employed have the general formula:

    Ru(CO)HA(Z).sub.3                                          ( 1)

In this formula, A is a halogen atom, preferably a chlorine or bromine atom, more preferably a chlorine atom or a hydrogen atom. The group Z is a substituted phosphine group of the formula --PR₁ R₂ R₃. The groups R₁, R₂ and R₃ may be the same or different and are alkyl and/or alkyl groups, preferably selected from methyl, ethyl, C₆ to C₁₀ aryl groups and C₇ to C₁₂ aralkyl groups. More preferably, each of R₁, R₂ and R₃ is a phenyl group, so that Z is a triphenylphosphine group. Compounds corresponding to formula (1) are air stable and catalytically active. Specific examples of particularly preferred compounds corresponding to formula (1) comprise carbonylchlorohydrido(tristriphenylphosphine)ruthenium (II) and carbonyldihydrido(tristriphenylphosphine)ruthenium (II). Complexes according to formula (1) may be readily synthesized by routine procedures.

This first group of complexes may be modified further by reacting with appropriate carboxylic acids to provide carbonylcarboxylato-derivatives of ruthenium (II), and thereby provide a second class of ruthenium complexes useful in the process of the invention. The coordinated properties of the carboxylate ligand-containing complexes, combining high catalyst stability with relatively high catalytic activity, render them particularly effective in the process of the present invention.

The suitable carbonylcarboxylato-derivatives of ruthenium(II) which are employed herein correspond to the general formula:

    Ru(CO)XY(Z).sub.2                                          ( 2)

in which X is a carboxylate group corresponding to the formula R₄ COO--, Y is a halogen atom, preferably a chlorine or bromine atom, a carboxylate group corresponding to the formula R₅ COO-- or a hydrogen atom, and Z is as defined above with respect to formula (1). The carboxylate groups R₄ COO-- and R₅ COO-- may be the same or different and comprise alkyl and aryl carboxylate groups, including halo-substituted alkyl and aryl carboxylate groups. Specific preferred carboxylate groups are mono-, di- and tri-halo substituted acetate, including ClCH₂ COO--, Cl₂ CHCOO--, Cl₃ CCOO-- and F₃ CCOO--, unsubstituted acetate i.e. CH₃ COO--, unsubstituted benzoate i.e. C₆ H₅ COO--, alkyl-substituted benzoate, including p-CH₃ C₆ H₄ COO-- and halo-substituted benzoate, including p-ClC₆ H₄ COO--.

Specific examples of particularly preferred compounds corresponding to formula (2) comprise chlorochloroacetato(carbonyl)bis(triphenylphosphine)ruthenium(II), chlorodichloroacetato(carbonyl)bis(triphenylphosphine)ruthenium(II), chlorotrichloroacetato(carbonyl)bis(triphenylphosphine)ruthenium(II), chlorotrifluoroacetato(carbonyl)bis(triphenylphosphine)ruthenium(II), chloroacetato(carbonyl)bis(triphenyl phosphine)ruthenium(II), chlorobenzoato(carbonyl)bis(triphenylphosphine)ruthenium(II), bromobenzoato(carbonyl)bis(triphenylphosphine)ruthenium(II), bis-(p-chlorobenzoato)carbonylbis(triphenylphosphine)ruthenium (II), hydrido-p-toluato(carbonyl)bis(triphenylphosphine)ruthenium(II), chlorobenzoato(carbonyl)bis(triethyl phosphine)ruthenium(II), and chlorobenzoato(carbonyl)bis(diphenylmethylphosphine)ruthenium(II).

Another class of ruthenium complexes which may be employed have the general formula:

    RuT(CO)(NO)(Z).sub.2                                       ( 3)

In this formula, T is a halogen atom, preferably a chlorine or bromine atom, more preferably a chlorine atom. The group Z is a substituted phosphine group of the formula --PR₁ R₂ R₃, as discussed in detail above with respect to the compounds of formula (I). A particularly preferred compound asccording to formula (3) is chloro carbonyl(nitrosyl)bis(triphenylphosphine)ruthenium (II).

Further classes of ruthenium complexes useful in the present invention have the general formula:

    RuT(NO)(Z).sub.2                                           ( 4)

    RuH(NO)(Z).sub.3                                           ( 5)

    Ru(NO).sub.2 (Z).sub.2                                     ( 6)

wherein T is a halogen atom as discussed above with respect to compounds of formula (3) and Z is a substituted phosphine group as discussed above with respect to compounds of formula (1). A preferred compound according to formula (4) is chloro(nitrosyl)bis(triphenylphospine)ruthenium (II). A preferred compound according to formula (5) is nitrosylhydrido(tris-triphenylphosphine)ruthenium (II). A preferred compound according to formula (6) is dinitrosyl bis(triphenylphosphine)ruthenium (II).

None of the complexes of formulae (1) to (6) are disclosed or suggested in the prior art as useful to effect selective hydrogenation of carbon-carbon double bonds in copolymers of a conjugated diene and one or more copolymerizable monomers. The only prior art of which the applicants are aware which discloses ruthenium complexes for such a purpose is the aforementioned U.S. Pat. No. 4,631,315 and German O.S. No. 3,529,252. In comparison to formulae (1) to (6), this prior art does not disclose complexes containing carbonyl ligands.

Preparative procedures for the formation of the ruthenium carbonyl complexes used in the present invention are described in the literature, for example, by Robinson et al, J. Chem-Soc. Dalton Trans., pp. 1912 to 1920 (1973). The hydrido- and carbonyl-carboxylatoruthenium(II) complexes may be prepared by such procedures, or may be generated in situ in the medium in which the selective hydrogenation is effected. For example, the carbonyl chlorohydridotris(triphenylphosphine)ruthenium(II) complex may be synthesized via aldehyde decarbonylation with dichlorotris(triphenylphosphine)ruthenium(II) complex, or may be generated in situ by adding dichloro tris(triphenylphosphine)ruthenium(II) and an approximately equal weight amount of propionaldehyde to a copolymer solution used in an atmosphere of hydrogen, optionally in the presence of added ligand, triphenylphosphine. Similarly, the carbonylcarboxylato-derivatives of formula (2) may be formed in situ from the complex of formula (1) and the respective carboxylic acid under a nitrogen atmosphere.

Preparative procedures for the formation of the nitrosyl containing complexes used in the present invention are described in the literature, for example, by Reed et al, Inorg. Synth., 16 (1976), p. 21; by Ahmad et al, Inorgan. Synth., 15, 1975, p. 45; by Wilson et al: J. Am. Chem. Soc., 93, (1971), p. 3068 and by Laing et al., J. Chem. Soc. (A), (1970), p. 2148.

In the present invention, the ruthenium carbonyl complexes of formulae (1) to (6) are used to effect selective hydrogenation of carbon-carbon double bonds in copolymers of a conjugated diene and one or more copolymerizable monomers. Such copolymers may be random, alternating or of block structure. Suitable conjugated dienes include C₄ to 6 conjugated dienes, such as butadiene, isoprene, dimethylbutadiene and piperylene. Suitable copolymerizable monomers include acrylonitrile and methacrylonitrile, alkenylaromatic hydrocarbons, such as styrene and α-methylstyrene, and C₃ to 6 α,β-unsaturated mono- or polycarboxylic acids, such as itaconic, fumaric, maleic, acrylic and methacrylic acids.

Preferred copolymers to which the present invention may be applied include butadiene-acrylonitrile copolymer, butadiene-methacrylonitrile copolymer, copolymers of butadiene with acrylontrile or methacrylonitrile and one or more of the C₃ to 6 α,β-unsaturated carboxylic acids, isoprene-acrylonitrile copolymer, isoprene-methacrylonitrile copolymer, and AB, ABA and ABCBA block copolymers wherein A is butadiene or isoprene, B is styrene or α-methylstyrene and C may be a coupling agent residue.

The selective hydrogenation is effected in any convenient manner in a solvent for the copolymer containing the catalyst. The copolymer is dissolved in the solvent and the resulting solution is degassed. The reaction vessel containing the copolymer solution is pressurized with hydrogen gas and the catalyst is added to and dissolved in the solution. Alternatively, the catalyst is added to and dissolved in the copolymer solution and then the reaction vessel may be pressurized with hydrogen. The reaction vessel is rapidly heated to the desired temperature and agitation is initiated. The hydrogenation reaction is allowed to proceed for the desired length of time with the hydrogen pressure preferably held constant. Upon completion of the hydrogenation reaction, the hydrogenated copolymer may be recovered by any convenient method.

The reaction vessel is pressurized with gaseous hydrogen usually from about 0.5 to about 7 MPa and preferably about 2.5 to about 5.0 MPa. It is preferred to employ pure hydrogen but hydrogen containing small amounts of inert gases, such as nitrogen, also may be used.

The hydrogenation reaction usually is effected at a temperature of about 80° to about 200° C., preferably about 110° to about 155° C. Under the preferred conditions of temperature and pressure, essentially complete hydrogenation of the carbon-carbon double bonds may be achieved in about 2 to about 9 hours, depending on the catalyst, temperature and pressure used. By using suitable conditions of time and temperature, it is possible to obtain copolymers which are only partially hydrogenated. The degree of hydrogenation may be adjusted to suit the requirements for the product required.

The concentration of ruthenium complex catalyst employed in the hydrogenation process usually ranges from about 0.1 to about 4 wt.% of polymer. High loadings of ruthenium catalyst may result in an undesirable isomerization of the Δ⁴,5 -unsaturated nitrile bonds to the stable α,β-unsaturated nitrile moiety. Accordingly, it is preferred to employ less than about 0.8 wt.% of the ruthenium complex catalyst when hydrogenating acrylonitrile-butadiene copolymers, since the undesirable isomerization is avoided at such catalyst levels. In addition, such isomerization may be reversed for a polymer produced at excessive levels of catalyst by effecting further hydrogenation of the product at catalyst levels of 0.8 wt.% or below or by effecting further hydrogenation in the presence of a rhodium complex catalyst of the type described in the above-mentioned U.S. Pat. No. 4,503,196, preferably HRh(PPh₃)₄ or ClRh(PPh₃)₃.

Some cross-linking or gel formation may occur during the selective hydrogenation process. Such gel formation has been observed when hydrogenating NBR with carbonylchlorohydridotris(triphenylphosphine)ruthenium (II) or chloroacetato(carbonyl)bis(triphenylphosphine)ruthenium(II) complexes. However, gel formation may be avoided by the addition of gel formation-inhibiting ligand compounds to the copolymer solution containing such catalysts. The amount of ligand compound added may be from about 1.0 to about 2.0 wt.% of the copolymer and the weight ratio of added ligand compound to ruthenium complex catalyst may vary from about 1:1 to about 2:1. Ligand compounds which are suitable for this purpose include phosphines and arsines, for example, triphenylphosphine and triphenylarsine, as well as a variety of carboxylic acids, for example, acetic acid, chloracetic acid, benzoic acid and p-chlorobenzoic acid for a copolymer solution in chlorobenzene.

The solvent used in the process of the present invention may be any organic solvent in which the copolymer, catalyst and ligand compounds are soluble and which is not adversely affected by the hydrogenation conditions. Such suitable solvents include aryl hydrocarbons and their alkyl and halo derivatives, such as benzene, toluene, xylene, chlorobenzene and dichlorobenzene, or aliphatic ethers, such as tetrahydrofuran and dioxane, or ketones, such as methylethylketone (MEK). When employed, MEK is reduced to some extent to 2-butanol under the reaction conditions used but this does not interfere with the desired hydrogenation of the copolymer.

It is known from the data presented in U.S. Pat. No. 4,631,315 that the presence of low molecular weight ketones decreases gel formation during selective hydrogenation of carbon-carbon double bonds using ruthenium complexes. We have confirmed that this result also is obtained for the ruthenium complexes described herein which tend to cause gel formation. Mixed solvents also may be used, in which one component is a low molecular weight ketone and the other is a hydrocarbon solvent, for example, methyl ethyl ketone and chlorobenzene in a volume ratio ranging from about 1:10 to about 10:1.

The hydrogenation products of the process of the invention are vulcanizable elastomers, the vulcanizates of which may be used in applications requiring resistance to oxidizing conditions at elevated temperatures for extended periods of time, for example, the various hoses and seals used in the engine compartment of an automobile.

The hydrogenated copolymers may be vulcanized using conventional peroxide or peroxide/sulfur curing systems. It is preferred to use vulcanizates in which from about 50 to about 99.95 percent, more preferably from about 95 to about 99.95 percent, and most preferably about 99 to about 99.95 percent of the carbon-carbon double bonds in the copolymer have been hydrogenated.

DESCRIPTION OF PREFERRED EMBODIMENTS

A first preferred embodiment of the process of the present invention is a homogeneous hydrogenation process wherein the hydrogenation is carried out with copolymer and catalyst dissolved in the solvent in a stainless steel autoclave. The copolymer may be dissolved in the organic solvent and the resulting solution purged, degassed and pressured with hydrogen gas. The reaction vessel is heated rapidly to the desired temperature, agitation initiated followed by catalyst addition. Upon completion of the reaction, the hydrogenated copolymer may be recovered by any convenient method well known in the art. For example, the reaction mixture may be mixed with an alcohol or contacted with hot water and/or steam in order to precipitate the copolymer which is then separated, washed if desired, and dried e.g. under vacuum. If desired the catalyst may be recovered by the method described in U.S. Pat. No. 3,545,963. Preferred catalysts for hydrogenating NBR in this preferred embodiment in stainless steel autoclave include the carbonylruthenium(II) complexes mentioned above, except RuHCl(CO)(PPh₃)₃ and Ru(CH₃ COO)Cl(CO)(PPh₃)₂, which are less preferred since they result in gel formation.

In another preferred embodiment of the process of the present invention, the copolymer is hydrogenated with RuHCl(CO)(PPh₃)₃ or Ru(CH₃ COO)Cl(CO)(PPh₃)₂ as the catalyst in the presence of the ligands triphenyl phosphine or acetic acid respectively, added to the copolymer solution to prevent crosslinking in the NBR before quantitative hydrogenation of the C═C unsaturation is achieved.

In yet another preferred embodiment of the process of the present invention, the copolymer is hydrogenated with carbonylcarboxylatoruthenium(II) complexes generated in situ from hydridocarbonylruthenium(II) derivatives and carboxylic acids, added to copolymer soluton in organic solvents. The preferred ratio of ruthenium(II) complex to carboxylic acid in this embodiment preferably is from about 1:0.1 to about 1:1.

In yet another preferred embodiment of the process of the present invention, the copolymer is hydrogenated with chloro carbonyl(nitrosyl)bis(triphenyl phosphine)ruthenium (II) added to copolymer solution in a ketone-containing solvent, such as methyl ethyl ketone.

EXAMPLES Example 1

In this and succeeding Examples, the copolymers which were hydrogenated are listed in the following Table I, in which the composition figures are given in percent by weight:

                  TABLE I                                                          ______________________________________                                         Copolymer                                                                              Composition                                                            ______________________________________                                         I       Acrylonitrile-butadiene copolymers containing                                  66 percent butadiene and sold under the trade                                  marks (a) Krynac 34.50 (b) Krynac 803 (c) Krynac                               XF-300 by Polysar Ltd.                                                 II      An acrylonitrile-butadiene copolymer                                           containing 64 percent butadiene and sold under                                 the trade mark Krynac 825 by Polysar Ltd                               III     An acrylonitrile-butadiene copolymer                                           containing 62 percent butadiene and sold under                                 the trade mark Krynac 38.50 by Polysar Ltd.                            IV      An acrylonitrile-butadiene copolymer                                           containing 60 percent butadiene and sold under                                 the trade mark Krynac 40.65 by Polysar Ltd.                            V       An acrylonitrile-isoprene copolymer containing                                 66 percent isoprene and sold under the trade                                   mark Krynac 833 by Polysar Ltd.                                        VI      A carboxylated acrylonitrile-butadiene                                         copolymer containing 64 percent butadiene and                                  sold under the trade mark Krynac 221 by                                        Polysar Ltd.                                                           VII     A carboxylated acrylonitrile-butadiene                                         copolymer containing 66 percent butadiene and                                  sold under the trade mark Krynac 110-C by                                      Polysar Ltd.                                                           VIII A styrene-butadiene-styrene, ABA block                                            copolymer containing 72 percent butadiene and                                  sold by Aldrich Chemical Company Inc.                                  IX      A styrene-butadiene linear AB block copolymer                                  containing 75 percent butadiene and sold under                                 the trade mark Solprene 1205 by Shell Chemical                                 Company.                                                               X       A styrene-butadiene, linear AB block copolymer                                 containing 70 percent butadiene and sold under                                 the trade mark Solprene 308 by Shell Chemical                                  Company.                                                               XI      A styrene-butadiene-styrene, radial ABA block                                  copolymer containing 70 percent butadiene and                                  sold under the trade mark Solprene 411 by                                      Shell Chemical Company.                                                ______________________________________                                    

Acrylonitrile-butadiene copolymers were hydrogenated using carbonylchlorohydridotris(triphenyl phosphine)ruthenium(II) complex with chlorobenzene as solvent in a stainless steel autoclave. Improvement in the process was sought in order to prevent gel formation during hydrogenation. This was accomplished by either adding a ligand compound such as triphenylphosphine or a carboxylic acid.

The copolymer was dissolved in a desired organic solvent (chlorobenzene) with stirring in a 300 ml glass liner. In runs Nos. 2, 3, 4 and 5 a ligand compound was added to the copolymer solution. The catalyst was weighed and placed into a catalyst addition device. The stainless steel (SS 316) autoclave was assembled and the solution degassed by bubbling hydrogen gas through the solution for 5 minutes. The autoclave was purged repeatedly by charging with hydrogen to about 0.7 MPa and then releasing the pressure. The autoclave was pressured with hydrogen to about 1.5 MPa and heated rapidly to 140° C. with agitation. After the temperature stabilized, the catalyst addition device was pressurized to 4.1 MPa with hydrogen in order to introduce the catalyst into the solution. The reaction was allowed to proceed for the desired length of time. Hydrogen gas was added as required to maintain pressure essentially constant throughout the reaction period.

After the desired reaction period, the autoclave was cooled in a cold water bath, depressurized and opened. A volume of iso-propanol equal to about 3 times the volume of solvent used in the reaction was added to the reaction product. The hydrogenated product which precipitated out of solution was separated by filtration, washed with iso-propanol and dried under vacuum.

The hydrogenated product was dissolved in deuterated chloroform and analyzed by proton NMR to determine the amount of hydrogenation of the carbon-carbon double bonds.

In runs Nos. 2 and 3, some isomerization of Δ⁴,5 unsaturated nitrile bonds in NBR to α,β-unsaturated nitrile moiety occurred in the course of the hydrogenation reaction. The I.R. spectrum of isomerized product exhibited two nitrile absorption bands at 2240 cm⁻¹ and 2220 cm⁻¹, attributed to the nitrile function and the conjugated nitrile function respectively. The presence of conjugated nitrile function was further substantiated by the presence of a multiplet centered at 6.2 ppm in the proton NMR spectrum attributed to isomerized protons. The proton NMR spectrum for such hydrogenated NBRs showed no resonance due to olefinic protons.

The amount of catalyst, ligand compound and copolymer used in the runs are shown in the following Table II:

                                      TABLE II                                     __________________________________________________________________________                         Added Ligand                                                                              Reaction                                                                            Percent                                    Run.sup.a,b                                                                        Copolymer                                                                            Catalyst  Compound   Time Hydro-                                     No. Type  Type      Type   Conc.                                                                              (Hour)                                                                              genation                                   __________________________________________________________________________     1   Ic    HRuCl(CO)(PPh.sub.3).sub.3                                                               --     --  3    90.sup.c                                   2   III   HRuCl(CO)(PPh.sub.3).sub.3                                                               PPh.sub.3                                                                             1.3 4    95.sup.d                                   3   III   RuCl.sub.2 (PPh.sub.3).sub.3                                                             PPh.sub.3 and                                                                         1.3 7    94.sup.e                                                       C.sub.2 H.sub.5 CHO                                                                   1.3                                                 4   Ia    HRuCl(CO)(PPh.sub.3).sub.3                                                               C.sub.6 H.sub.5 COOH                                                                  0.2 2.5  99+                                        5   III   HRuCl(CO)(PPh.sub.3).sub.3                                                               C.sub.2 H.sub.5 COOH                                                                  0.2 1.8  99+                                        __________________________________________________________________________      .sup.a 1.7 percent by weight solution of copolymer in 90 ml of                 chlorobenzene; 0.8 percent by weight of catalyst with respect to               copolymer.                                                                     .sup.b Temperature 140° C., Total pressure = 4.1 MPa (hydrogen)         .sup.c At this conversion, some gel formation occurred                         .sup.d 5 percent unsaturation left due to isomerization of C = C to            conjugated nitrile moiety                                                      .sup.e 6 percent isomerization as in d                                   

In this Example and those that follow, the concentration of the copolymer in solution is in percent by weight based on the total volume on the solution while the concentration of the catalyst and the ligand compounds are percent by weight based on the copolymer. The percent hydrogenation figures given are percent of the carbon-carbon double bonds of the copolymer which has been hydrogenated. When a value of 99+ is given, the amount of hydrogenation is greater than 99.5 percent and less than or equal to 99.95 percent, i.e. essentially complete.

Example 2

This Example illustrates a homogeneous solution hydrogenation process of the present invention using chlorotris(triphenylphosphine)rhodium(I) or hydridotetra kis(triphenylphosphine)rhodium(I) to completely hydrogenate isomerized hydrogenated product obtained in Example 1 above using carbonylchlorohydridotris(tri phenylphosphine)ruthenium(II) complex in the presence of ligand i.e. triphenylphosphine.

To the reaction mixture of run No. 2 in Example 1, was added hydridotetrakis(triphenylphosphine)rhodium(I) and triphenylphosphine (2.0 and 20 percent by weight respectively based on the weight of the copolymer) at 110° C. and 4.1 MPa hydrogen pressure. After 9 hours of reaction I.R. spectrum and ¹ H NMR showed complete disappearance of isomerized moiety. The reaction was worked up as outlined in Example 1. ¹ H NMR indicated 99+% hydrogenation.

Example 3

This Example illustrates a homogeneous solution hydrogenation process of the present invention wherein the copolymer Ia from Table I has been hydrogenated with dihydridocarbonylruthenium(II) complex i.e. RuH₂ (CO)(PPh₃)₃.

In this run, 90 ml of 1.7 percent by weight solution in chlorobenzene of copolymer Ia from Table I was hydrogenated in the presence of 0.8 percent by weight of the dihydridocarbonylruthenium(II) complex at 140° C. temperature and 4.1 MPa hydrogen pressure. After 2 hours, reaction was terminated and the hydrogenated product was recovered following the work up procedure outlined in Example 1. The degree of hydrogenation was determined to be 99+% by ¹ H NMR.

Example 4

This Example illustrates a homogeneous solution hydrogenation process of the present invention using carbonylcarboxylato derivates of ruthenium (II) of the general formula Ru(CO)XY(Z)₂ where X=carboxylate; Y=chloride or hydride; Z=trialkyl, aryl, or aryl-alkyl phosphine. In this method, copolymers I to XI from Table I were hydrogenated. The procedure and reaction conditions used were the same as outlined in Example 1, except no ligand compound was added to copolymer solutions.

The product in each case was analyzed to proton NMR to determine the amount of hydrogenation of the carbon-carbon double bonds. Analysis by ¹³ C NMR and IR spectrum showed that no hydrogenation occurred of the nitrile groups of copolymers I through VII of Table I. Analysis by IR spectrum of the hydrogenated product also revealed that no hydrogenation occurred of the acid groups of copolymers VI and VII. The amount of catalyst, copolymer and solvent used are given in the following Table III:

                                      TABLE III                                    __________________________________________________________________________                                      Reaction                                                                            Percent                                  Run.sup.a,b                                                                        Copolymer                                                                             Catalyst              Time Hydro-                                   No. Type                                                                              Conc.                                                                              Type              Conc.                                                                              (Hour)                                                                              genation                                 __________________________________________________________________________      1  Ia 1.7 RuCl(CO)(ClCH.sub.2 COO)(PPh.sub.3).sub.2                                                        0.8 2.5  99 +                                      2  Ia 1.7 RuCl(CO)(ClCH.sub.2 COO)(PPh.sub.3).sub.2                                                        0.4 3.9  99 +                                      3  III                                                                               1.7 RuCl(CO)(C1CH.sub.2 COO)(PPh.sub.3).sub.2                                                        0.8 2.4  99 +                                      4  III                                                                               1.7 RuCl(CO)(ClCH.sub.2 COO)(PPh.sub.3).sub.2                                                        0.4 4.5  99 +                                      5  Ib 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 1.8  99 +                                      6  Ic 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 1.9  99 +                                      7  II 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 2.3  99 +                                      8  III                                                                               1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 2.6  99 +                                      9  III                                                                               3.3 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 6.2  98                                       10  IV 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 2.3  99 +                                     11  V  1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 6    99 +                                     12  VI 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 23   94                                       13  VII                                                                               1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   0.8 2.3  99 +                                     14  IX 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   1.0 2.0  99 +                                     15  X  1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   1.0 1.8  99 +                                     16  XI 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   1.0 2.2  99 +                                     17  VIII                                                                              1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(PPh.sub.3).sub.2                                                   1.6 1.5  99 +                                     18  Ia 1.7 RuCl(CO)(C.sub.6 H.sub.5 COO)(P(CH.sub.3)Ph.sub.2).sub.2                                         0.8 19   93.sup.c                                 19  III                                                                               1.7 RuCl(CO)(CH.sub.3 COO)(PPh.sub.3).sub.2                                                          0.8 2    85.sup.d                                 20  III                                                                               1.7 Ru(CO)(p-ClC.sub.6 H.sub.4 COO).sub.2 (PPh.sub.3).sub.2                                          0.8 2    99 +                                     21  III                                                                               1.7 HRu(CO)(p-CH.sub.3 C.sub.6 H.sub.4 COO)(PPh.sub.3).sub.2                                         0.8 1.8  99 +                                     __________________________________________________________________________      .sup.a Percent by weight solution of copolymer in 90 ml of chlorobenzene       .sup.b Temperature 140° C. Total pressure = 4.1 MPa (hydrogen)          .sup.c 7 percent unsaturation left due to isomerization of C = C to            conjugated nitrile moiety                                                      .sup.d At this conversion some gel formation occurred                    

Example 5

This Example illustrates a homogeneous solution hydrogenation process of the present invention wherein crosslinking in the NBR during the course of hydrogenation reaction with chloroacetato(carbonyl)bis(triphenylphosphine)ruthenium(II) i.e. RuCl(CO)(CH₃ COO)(PPh₃)₂ is avoided by adding ligand compound, namely acetic acid. The procedure used was as described in Example 1, except copolymer III from Table I was used.

In this run, 90 ml of 1.7 percent by weight solution of copolymer III in chlorobenzene was added 0.8 wt. percent (based on the weight of copolymer III) of acetic acid. After purging, degassing the system with hydrogen and adjusting the temperature at 140° C., 0.8 wt. percent (based on the weight of copolymer III) of RuCl(CO)(CH₃ COO)(PPh₃)₂ was added and the reaction was followed by NMR until complete disappearance of olefinic protons was observed. After 2.5 hours of reaction, following the workup procedure outlined in Example 1, a completely hydrogenated product (99+%) was obtained.

Example 6

This Example illustrates the use of a homogeneous solution hydrogenation process of the present invention to produce hydrogenated copolymer with varying degree of hydrogenation of the carbon-carbon double bonds. The procedure and reaction conditions used were as described in Example 1, except that copolymer III from Table I and chlorochloroacetato(carbonyl)bis(triphenylphosphine)ruthenium(II) i.e. RuCl(CO)(ClCH₂ COO)(PPh₃)₂ as a catalyst, were used in this case and the reaction temperature was maintained at 125° C.

In this Example, 1.5 g of copolymer III of Table I was dissolved in 90 ml of chlorobenzene and the solution was degassed with hydrogen after assembling the autoclave. The autoclave was heated rapidly to 125° C., pressured to 4.1 MPa with H₂ and 0.8 weight percent of catalyst (based on the weight of copolymer) was added. Samples were withdrawn during the course of the reaction and analyzed by proton NMR for the percent of carbon-carbon double bonds hydrogenated. Analytical results are given in the following Table IV:

                  TABLE IV                                                         ______________________________________                                         Reaction Time (hr)                                                                            Percent Hydrogenation                                           ______________________________________                                         0.5            35.0                                                            0.7            52.0                                                            1.3            84.0                                                            2.2            94.0                                                            4.3            98.0                                                            ______________________________________                                    

The results of the above Table IV demonstrate that by stopping the reaction at any desired point and recovering the product as usual, a partially hydrogenated product may be obtained.

Example 7

This Example illustrates a homogeneous solution hydrogenation process of the present invention using a range of solvents. The procedure used was that described in Example 1. In each run, 90 ml of 1.7 percent by weight solution of copolymers Ic or III in a suitable organic solvent was hydrogenated in the presence of 12 mg (0.8 percent by weight with respect to copolymer Ic or III) of chlorobenzoato(carbonyl)bis(triphenylphosphine)ruthenium(II). The hydrogen pressure was 4.1 MPa and reaction temperature was maintained at 140° C. The results obtained are reproduced in the following Table V:

                  TABLE V                                                          ______________________________________                                                                              Percent                                   Run.sup.a                                                                           Copolymer Solvent       Reaction                                                                               Hydro-                                    No.  Type.sup.b,c                                                                             Type          Time (Hr)                                                                              genation                                  ______________________________________                                         1    III       Chlorobenzene 1.8     99+                                       2    III       o-Dichlorobenzene                                                                            3.0     99+                                       3    Ic        Benzene       6.0     99+                                       4    Ic        Toluene       10.5    99                                        5    Ic        p-Xylene      12      99+                                       6    Ic        Methylethylketone                                                                            2.3     99+                                       7    Ic        Tetrahydrofuran                                                                              3.5     99+                                       ______________________________________                                          .sup.a 1.7 weight percent solution in 90 ml of solvent                         .sup.b 0.8 weight percent of RuCl(CO)(C.sub.6 H.sub.5                          COO)(PPh.sub.3).sub.2 with respect to copolymer                                .sup.c 140° C. and 4.1 MPa hydrogen pressure                      

As may be seen from the results of above Table V, a variety of solvents may be used to effect the hydrogenation process.

Example 8

This Example illustrates a homogeneous hydrogenation process of the present invention using a range of temperatures. The procedures used was as that of Example 1, except copolymer III of Table I and chlorobenzoato(carbonyl)bis(triphenylphosphine)ruthenium (II) i.e. RuCl(CO)(C₆ H₅ COO)(PPh₃)₂ as catalyst, were employed in the hydrogenation process. The autoclave was charged with hydrogen to 4.1 MPa and after completion of reaction, the reaction solution was worked up as outlined in Example 1. The results obtained are shown in the following Table VI:

                  TABLE VI                                                         ______________________________________                                         Run.sup.a,b,c                                                                         Temperature   Reaction  Percent                                         No.    °C.    Time (Hr) Hydrogenation                                   ______________________________________                                         1      125           4.3       98.0                                            2      140           2.5       99+                                             3      155           1.4       99+                                             ______________________________________                                          .sup.a 1.7 weight percent of copolymer III in 90 ml chlorobenzene              .sup.b 0.8 weight percent of RuCl(CO)(C.sub.6 H.sub.5                          COO)(PPh.sub.3).sub.2 with respect to copolymer III                            .sup.c 4.1 MPa hydrogen pressure                                         

Example 9

This Example illustrates a homogeneous solution hydrogenation process of the present invention using a range of hydrogen pressure. The procedure used was that of Example 1, except copolymer III of Table I was used and the hydrogenation reaction was performed in the presence of chlorobenzoato(carbonyl)bis(triphenyl phosphine)ruthenium (II). The reaction conditions used and results obtained are shown in the following Table VII:

                  TABLE VII                                                        ______________________________________                                         Run.sup.a,b,c                                                                          Hydrogen     Reaction   Percent                                        No.     Pressure (MPa)                                                                              Time (Hr)  Hydrogenation                                  ______________________________________                                         1       2.7          7.7        98.0                                           2       3.4          4.0        98.0                                           3       4.1          2.5         99+                                           ______________________________________                                          .sup.a 1.7 weight percent of copolymer III in 90 ml chlorobenzene              .sup.b 0.8 weight percent of RuCl(CO)(C.sub.6 H.sub.5                          COO)(PPh.sub.3).sub.2 with respect to copolymer III                            .sup.c 140° C. temperature                                        

Example 10

This Example illustrates a homogeneous solution hydrogenation process of the present invention using a range of catalyst concentration. The procedure used was that of Example 1, except that copolymer Ia of Table I was hydrogenated in the presence of chlorochloroacetato(carbonyl)bis(triphenylphosphine). The reaction conditions used and results obtained are shown in the following Table VIII:

                  TABLE VIII                                                       ______________________________________                                                                    Percent Percent                                     Run.sup.a                                                                           Catalyst.sup.b,c                                                                           Reaction  Hydrogen-                                                                              Unsaturation                                No.  Concentration                                                                              Time (Hr) ation   (Isomerization)                             ______________________________________                                         1    3.3         4.8       97.0    3.0                                         2    1.7         2.0       99.0    1.0                                         3    0.8         2.5       99+     0                                           4    0.4         3.9       99+     0                                           ______________________________________                                          .sup.a 1.7 weight percent of copolymer III in 90 ml chlorobenzene              .sup.b wt. percent of RuCl(CO)(ClCH.sub.2 COO)(PPh.sub.3).sub.2 based on       the wt. of copolymer Ia                                                        .sup.c Temperature 140° C. and 4.1 MPa hydrogen pressure          

The unsaturation obtained owing to isomerization could not be removed even after allowing the reaction to proceed for longer periods of time. These results show that isomerization can be avoided, however, at catalyst concentrations of 0.8 wt.% and below.

Example 11

This Example illustrates the use of a mixed solvent system to avoid gel formation.

The procedure of Example 1 was used to effect hydrogenation of copolymer III in a mixed solvent comprising methyl ethyl ketone and chlorobenzene, with or without added phosphine, using HRuCl(CO)PPh₃)₃ or catalyst. The reaction conditions and results obtained are set forth in the following Table IX:

                                      TABLE IX                                     __________________________________________________________________________                                  Percent                                                                 Reaction                                                                              Hydrogen-                                         Run.sup.a,b,c                                                                       solvent    Ligand                                                                               Time (Hr)                                                                             ation Gel                                         __________________________________________________________________________     1    30 ml MEK + 70 ml                                                                         none  5      99+   none                                             chlorobenzene                                                             2    30 ml MEK + 70 ml                                                                         0.08 g                                                                               7      99+   none                                             chlorobenzene                                                                             phophine                                                       __________________________________________________________________________      .sup.a 2.0 weight percent of copolymer III                                     .sup.b 3.5 weight percent of HRuCl(CO)(PPh.sub.3).sub.3 w.r.t. copolymer       III                                                                            .sup.c 150° C. temperature, 5.5 MPa hydrogen pressure.            

The results set forth in the above Table IX illustrate quantitive hydrogenation without gel formation using a mixed solvent system.

Example 12

This Example illustrates the use of nitrosyl containing complexes in processes according to the present invention.

The procedure of Example 1 was used to effect hydrogenation of copolymer III in methyl ethyl ketone solvent. The concentration of copolymer III was approximately 5 weight percent (weight copolymer/weight solvent basis). The reaction conditions used and results obtained are shown in the following Table X:

                                      TABLE X                                      __________________________________________________________________________                   Catalyst            Percent                                                    Concentration %                                                                         Pressure                                                                           time   Hydro-                                       Run Catalyst  (wt/wt/polymer)                                                                         (MPa)                                                                              (hr.)                                                                              Gel                                                                               genation                                     __________________________________________________________________________     1 RuCl(CO)(NO)(PPh.sub.3).sub.2                                                              1.0      6.3  5  none                                                                               99+                                         2 RuCl(NO)(PPh.sub.3).sub.2                                                                  1.0      7.3 50  none                                                                              92                                           3 RuH(NO)(PPh.sub.3).sub.3                                                                   1.0      6.3 20  none                                                                              97                                           4 Ru(NO).sub.2 (PPh.sub.3).sub.2                                                             1.2      4.1 11  none                                                                              84                                           __________________________________________________________________________

SUMMARY OF DISCLOSURE

In summary of this disclosure, the present invention provides a novel process for effecting hydrogenation of carbon-carbon double bond unsaturation in conjugated diene copolymers using certain ruthenium complexes. Gel production and isomerization can be suppressed by varying the reaction conditions. Modifications are possible within the scope of this invention. 

What we claim is:
 1. In a process for the selective hydrogenation of the carbon-carbon double bonds in a copolymer of a conjugated diene and at least one copolymerizable monomer, the improvement which comprises effecting said hydrogenation in the presence of at least one divalent ruthenium complex selected from the group consisting of:(a) a ruthenium complex of the general formula:

    RuT(CO)(NO)(Z).sub.2                                       ( 1)

wherein T is a halogen atom and Z is a --PR₁ R₂ R₃ group in which R₁, R₂ and R₃ may be the same or different and are selected from alkyl and aryl groups, (b) a ruthenium complex of the general formula:

    RuT(NO)(Z).sub.2                                           ( 2)

wherein T and Z are as defined above, (c) a ruthenium complex of the general formula:

    RuH(NO)(Z).sub.3                                           ( 3)

wherein Z is as defined above, and (d) a ruthenium complex of the general formula:

    Ru(NO).sub.2 (Z).sub.2                                     ( 4)

wherein Z is as defined above.
 2. The process of claim 1 wherein said ruthenium complex is one of the general formula:

    RuCl(CO)(NO)(Z).sub.2                                      ( 1)

in which Z is the group PR₁ R₂ R₃ and R₁, R₂ and R₃ are the same or different and selected from methyl, ethyl, C₆ to C₁₀ aryl and C₇ to C₁₂ aralkyl.
 3. The process of claim 2 wherein each of R₁, R₂ and R₃ is a phenyl group.
 4. The process of claim 1 wherein said ruthenium complex is one of the general formula:

    RuCl(NO)(Z).sub.2                                          ( 2)

in which Z is the grouup PR₁ R₂ R₃ and R₁, R₂ and R₃ are the same or different and selected from methyl, ethyl, C₆ to C₁₀ aryl and C₇ to C₁₂ aralkyl.
 5. The process of claim 4 wherein each of R₁, R₂ and R₃ is a phenyl group.
 6. The process of claim 1 wherein said ruthenium complex is one of the general formula:

    RuH(NO)(Z).sub.3                                           ( 3)

in which Z is the group PR₁ R₂ R₃ and R₁, R₂ and R₃ are the same or different and selected from methyl, ethyl, C₆ to C₁₀ aryl and C₇ to C₁₂ aralkyl.
 7. The process of claim 6 wherein each of R₁, R₂ and R₃ is a phenyl group.
 8. The process of claim 1 wherein said ruthenium complex is one of the general formula:

    Ru(NO).sub.2 (Z).sub.2                                     ( 4)

in which Z is the group PR₁ R₂ R₃ and R₁, R₂ and R₃ are the same or different and selected from methyl, ethyl, C₆ to C₁₀ aryl and C₇ to C₁₂ aralkyl.
 9. The process of claim 8 wherein each of R₁, R₂ and R₃ is a phenyl group. 